The present invention relates to articulated multi-unit railroad cars, and in particular to side bearing arrangements associated with a shared truck supporting a pair of adjacent car units.
In some multi-unit freight cars a shared truck supports an end of each of a pair of adjacent car units which are connected to each other and to the shared truck by an articulating coupling. Such a shared truck has a generally vertical turning axis, and much of the weight of the respective end of each of the adjacent car units is carried to the shared truck through a center bearing where the articulating coupling interconnecting the two car units with each other rests atop a member of the shared truck, usually a transversely oriented truck bolster. Side bearings, located laterally outward from the center bearing, may carry a portion of the weight of each car unit to the shared truck.
In the past, articulated multi-unit rail cars have utilized shared trucks, with adjacent car units interconnected by articulating couplings including respective male and female portions. Various arrangements of side bearings for articulated multi-unit railway cars are also shown in Weber U.S. Pat. No. 3,399,631, and Adams et al. U.S. Pat. No. 4,233,909, which show similar side bearings for each of a pair of car units carried by a single shared truck.
Friction generated in the center bearing and the side bearings resists turning movement of such a shared truck relative to the adjacent car units. A certain amount of friction is desirable to prevent a shared truck from turning too easily with respect to the adjacent car units when such a multi-unit railroad car is traveling along tangent track, especially when the railroad car is unloaded, since a side-to-side harmonic oscillation of the car, called hunting, may result from the truck turning too easily, and may ultimately cause derailment of such a car.
Also important, however, is that with each shared truck of an articulated multi-unit railroad car having to carry heavy loads, as the individual car units are loaded, for example, with long cargo containers stacked one upon another, the friction generated in the center bearings and side bearings of a shared truck is able to cause an undesirably great amount of resistance to turning the shared truck relative to the car units, so that the total truck turning moment required to cause the truck to turn relative to the car units, in order to follow curvature of the railroad track, is too great, and excessive forces may be transmitted to the truck structure. The occurrence of these high forces appears to be more likely in heavily loaded cars traveling at low speed and entering curved track where one rail is superelevated than at other times.
What is needed, then, is a bearing arrangement, for transferring loads from the respective interconnected ends of a pair of adjacent car units to a shared truck in an articulated multi-unit railroad car, which results in the shared truck being able to follow curved track at various speeds without transmitting excessive forces or spreading apart the rails of the track when the car is heavily laden, yet without excessive hunting when the car is operated empty.